84 lines
2.0 KiB
C++
84 lines
2.0 KiB
C++
/*
|
|
* Copyright (c) Facebook, Inc. and its affiliates.
|
|
*
|
|
* Licensed under the Apache License, Version 2.0 (the "License");
|
|
* you may not use this file except in compliance with the License.
|
|
* You may obtain a copy of the License at
|
|
*
|
|
* http://www.apache.org/licenses/LICENSE-2.0
|
|
*
|
|
* Unless required by applicable law or agreed to in writing, software
|
|
* distributed under the License is distributed on an "AS IS" BASIS,
|
|
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
* See the License for the specific language governing permissions and
|
|
* limitations under the License.
|
|
*/
|
|
|
|
#pragma once
|
|
|
|
#include <unordered_map>
|
|
#include <unordered_set>
|
|
|
|
#include <glog/logging.h>
|
|
|
|
namespace folly {
|
|
namespace observer_detail {
|
|
|
|
template <typename NodeId>
|
|
class GraphCycleDetector {
|
|
using NodeSet = std::unordered_set<NodeId>;
|
|
|
|
public:
|
|
/**
|
|
* Add new edge. If edge creates a cycle then it's not added and false is
|
|
* returned.
|
|
*/
|
|
bool addEdge(NodeId from, NodeId to) {
|
|
// In general case DFS may be expensive here, but in most cases to-node will
|
|
// have no edges, so it should be O(1).
|
|
NodeSet visitedNodes;
|
|
dfs(visitedNodes, to);
|
|
if (visitedNodes.count(from)) {
|
|
return false;
|
|
}
|
|
|
|
auto& nodes = edges_[from];
|
|
DCHECK_EQ(nodes.count(to), 0u);
|
|
nodes.insert(to);
|
|
|
|
return true;
|
|
}
|
|
|
|
void removeEdge(NodeId from, NodeId to) {
|
|
auto& nodes = edges_[from];
|
|
DCHECK(nodes.count(to));
|
|
nodes.erase(to);
|
|
if (nodes.empty()) {
|
|
edges_.erase(from);
|
|
}
|
|
}
|
|
|
|
private:
|
|
void dfs(NodeSet& visitedNodes, NodeId node) {
|
|
// We don't terminate early if cycle is detected, because this is considered
|
|
// an error condition, so not worth optimizing for.
|
|
if (visitedNodes.count(node)) {
|
|
return;
|
|
}
|
|
|
|
visitedNodes.insert(node);
|
|
|
|
if (!edges_.count(node)) {
|
|
return;
|
|
}
|
|
|
|
for (const auto& to : edges_[node]) {
|
|
dfs(visitedNodes, to);
|
|
}
|
|
}
|
|
|
|
std::unordered_map<NodeId, NodeSet> edges_;
|
|
};
|
|
} // namespace observer_detail
|
|
} // namespace folly
|